A Savannah teenager on Tuesday pleaded guilty to robbing two 14-year-olds at gunpoint in 2010. A co-defendant pleaded guilty to a reduced charge a day earlier.

Daminason Jackson, now 18, was sentenced to 20 years in prison with 12 to serve and an additional 14 years on probation for what Chatham County Superior Court Judge Timothy R. Walmsley called a “significant crime and one the court has to take very seriously.”

Jackson, who was 16 at the time of the crimes on Nov. 24, 2010, has been in custody since June 2011.

Walmsley said the fact a 16-year-old was running around with a gun was “disturbing to say the least.”

Assistant District Attorney Ann Elmore said Jackson was the gunman who put a weapon to the head of one of the victims and stole his bike and cellphone. The second victim also was robbed of his bike and cellphone. Neither was injured.

Elmore urged Walmsley to impose a sentence reflective of the fact Jackson robbed two victims with a gun.

“There was gratuitous violence in this case,” she told Walmsley. “He has accepted responsibility, and he should be credited with that.”

As part of the sentence, Elmore asked Walmsley to order the weapon used in the crimes be destroyed.

Defense attorney David Burns Jr. urged a sentence of 10 years — the minimum sentence — arguing a sentence of more time would prove nothing.

“He has accepted what he has done. He accepts that,” Burns said.

On Monday, co-defendant Vonzello Antonio Garnett, 20, was allowed to plead guilty to a reduced charge of robbery by intimidation in return for a 12-year sentence with 26 months in custody.

Part of his plea required Garnett to testify against Jackson.

The custody sentence from Walmsley allowed Garnett to walk free from the Chatham County jail where he had been held since December 2010.